a) Field of the Invention
The present invention relates to an air spray gun which is used to blow dry a painted surface of cold baked coating, and more particularly to an air spray gun, wherein a gap size of an air-taking ring can be adjusted according to an air blow rate.
b) Description of the Prior Art
Referring to FIG. 1, it shows a cutaway view of a conventional air spray gun, wherein the air spray gun 10 is composed of an air spray tube 101 and a grip 102, and the air spray tube 101 is assembled by a front tube 1011 and a rear tube 1012 into a unit which is not able to be disassembled. An interior of the front tube 1011 is formed with an air-discharge conduit 10111, a rear end on an outer wall of the front tube 1011 is formed with a groove 10112, and the front tube 1011 is formed with a screw-hole 10113 which is connected with the groove 10112. An interior at a rear end of the rear tube 1012 is formed with a slant air-suction conduit 10121 which is gradually converged inward, and a front end of the rear tube 1012 is provided with a flange 10122 which can be tightly assembled with the groove 10112 of the front tube 1011. Accordingly, after the aforementioned front tube 1011 has been assembled with the rear tube 1012, they cannot be disassembled, and an air-taking ring 1013 of a fixed gap is formed between a rear-end surface of the air-discharge conduit 10111 of the front tube 1011 and a front-end surface of the air-suction conduit 10121 of the rear tube 1012.
Upon using the aforementioned conventional structures, a screw-hole at a bottom of the air spray tube 101 is connected with a high-pressure air tube 103 which is then connected to an exterior air compressor (or air supply system). When external high-pressure air is fed into an annular air chamber which is formed by the groove 10112 of the air spray tube 101, the air will be spraying toward a front along the air-discharge conduit 10111 through the air-taking ring 1013, and air at an exterior of a rear-end opening of the air-suction conduit 10121 of the air spray tube 101 will be driven by a pressure difference to be sucked inward, such that a large quantity of air will be blown forward to blow dry a painted surface of cold baked coating, or to feed the air or blow dry for other purposes. In addition, in using the air spray gun, the rear end of the air spray tube 101 can be sheathed with a rear cap 104 having a filtering net 1041 to filter out impurities or dusts in the air, so as to prevent the impurities or dusts from being dipped on the painted surface.
However, the aforementioned prior art is provided with following shortcomings:                1. As the air-taking ring in the conventional air spray gun is a structure of a fixed gap, a magnitude of air discharge rate cannot be controlled by changing the gap size, resulting in that the air spray gun cannot be applied to all kinds of raw materials of different viscosities for the cold baked coating, thereby causing an inconvenience in usage.        2. As the air-taking ring is the structure of the fixed gap, when the air spray gun is connected with the external high-pressure air device or system, a lower end of the high-pressure air tube should be connected with a control valve which is then connected to the external high-pressure air device, and a valve or an axle part of the control valve will be pasted with a lubricant to maintain a good mobility. However, in using the air spray gun, the aforementioned lubricant is easy to be driven into the air spray tube by the high-pressure air which passes through the control valve, to blow toward the painted surface of water-style cold baked coating, which results in changes of chemical or physical properties of the painted surface, thereby affecting a quality of the painted surface, or even damaging an entire working surface.        3. Even that the air spray gun is sheathed with the rear cap having the filtering net, the dusts will be still accumulated inside the tubes under a long term of usage. As the front tube and the rear tube cannot be disassembled, it will not be easy to clean the dusts in the tubes. Accordingly, it is necessary to make improvement to the aforementioned prior art.        